Concept 10
Chromosomes carry genes.

Cross pure-bred pea plants to identify dominant flower color.

HI! You have a culture of fruit flies. You find a fly with a possible new trait: a female with an ebony body. You mate this ebony female with a brown body male. If the ebony trait is recessive, what color are the offspring? Offspring will have brown bodies. That is correct. Offspring will have ebony bodies. No, that is incorrect. Ebony is recessive. Offspring will have dark brown bodies. No, that is incorrect. Genes don't blend. Offspring will have brown and black stripes. No, that is incorrect. Try again. If the ebony body color is a recessive trait, then a cross with a brown body fly will give F1 offspring with brown bodies. This is in fact what you see. Next, you cross a male and a female from the F1. Ebony is recessive so for the genotype of these flies we'll use the small letter "e" for ebony and the big letter "B" for the dominant brown. Out of 200 offspring from this cross, 152 have brown bodies and 48 have ebony bodies. e = ebony B = brown Assuming that the flies are segregating in a Mendelian ratio, how many of the 152 brown body flies are heterozygous for ebony? none. No, the parents are heterozygous, some of the offspring must be heterozygous. 53. No, this is the number of homozgyous brown flies. 50. No, this is about half the number of heterozygous ebony flies. 99. That is correct. all 152. No, if all flies are heterozygous, there won't be any ebony flies. Heterozygous flies have two different alleles of a gene. In this case, there are 49 + 50 = 99 heterozygous flies (Be). These flies are still brown because brown is dominant. You also check the sex of these flies and notice that there are fairly equal numbers of males and females that have brown bodies and ebony bodies. With this information, you deduce that the ebony body trait is: a sex-linked dominant trait. No, ebony is a recessive trait and not linked to a sex chromosome. a sex-linked recessive trait. No, ebony is not a sex-linked trait. The number of ebony males equals the ebony females. a recessive trait not linked to a sex chromosome. That is correct. a dominant trait not linked to a sex chromosome. No, ebony is a recessive trait. not an inherited trait. No, ebony is an inherited trait. Ebony is a recessive trait; the F1 progeny of ebony and brown are brown. Ebony is not a sex-linked trait because body color is not dependent on sex.